The present invention relates to the use of thermosensitive, biodegradable hydrogels, consisting of a block copolymer of poly(d,1- or 1-lactic acid)(PLA) or poly(lactide-co-glycolide)(PLGA) and polyethylene glycol (PEG), for the sustained delivery of biologically active agents.
Due to recent advances in genetic and cell engineering technologies, proteins known to exhibit various pharmacological actions in vivo are capable of production in large amounts for pharmaceutical applications. Such proteins include erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF), interferons (alpha, beta, gamma, consensus), tumor necrosis factor binding protein (TNFbp), interleukin-1 receptor antagonist (IL-1ra), brain-derived neurotrophic factor (BDNF), kerantinocyte growth factor (KGF), stem cell factor (SCF), megakaryocyte growth differentiation factor (MGDF), osteoprotegerin (OPG), glial cell line derived neurotrophic factor (GDNF) and obesity protein (OB protein). OB protein may also be referred to herein as leptin.
Leptin is active in vivo in both ob/ob mutant mice (mice obese due to a defect in the production of the OB gene product) as well as in normal, wild type the OB gene product) as well as in normal, wild type mice. The biological activity manifests itself in, among other things, weight loss. See generally, Barinaga, xe2x80x9cObesexe2x80x9d Protein Slims Mice, Science 269: 475-476 (1995). See PCT International Publication Number WO 96/05309, xe2x80x9cModulators of Body Weight, Corresponding Nucleic Acids and Proteins, and Diagnostic and Therapeutic Uses Thereof,xe2x80x9d herein incorporated by reference in its entirety.
The other biological effects of OB protein are not well characterized. It is known, for instance, that in ob/ob mutant mice, administration of leptin results in a decrease in serum insulin levels, and serum glucose levels. It is also known that administration of leptin results in a decrease in body fat. This was observed in both ob/ob mutant mice, as well as non-obese normal mice. Pelleymounter et al., Science 269: 540-543 (1995); Halaas et al., Science 269: 543-546 (1995). See also, Campfield et al., Science269: 546-549 (1995) (Peripheral and central administration of microgram doses of leptin reduced food intake and body weight of ob/ob and diet-induced obese mice but not in db/db obese mice.) In none of these reports have toxicities been observed, even at the highest doses.
Preliminary leptin induced weight loss experiments in animal models predict the need for a high concentration leptin formulation with chronic administration to effectively treat human obesity. Dosages in the milligram protein per kilogram body weight range, such as 0.5 or 1.0 mg/kg/day or below, are desirable for injection of therapeutically effective amounts into larger mammals, such as humans. An increase in protein concentration is thus necessary to avoid injection of large volumes, which can be uncomfortable or possibly painful to the patient. unfortunately, native human leptin is known to be relatively insoluble in an aqueous solution at hysiological pH at concentrations of approximately 10 mg/mL and above, often resulting in adverse injection site reactions. Moreover, kidney anatomical abnormalities have been found to be associated with leptin administration in certain settings, e.g. PEG-leptin.
Because proteins such as leptin generally have short in vivo half-lives and negligible oral bioavailability, they are typically administered by frequent injection, thus posing a significant physical burden on the patient (injection site reactions are particular problematic with many leptin formulations) and associated administrative costs. As such, there is currently a great deal of interest in developing and evaluating sustained-release formulations. Effective sustained-release formulations can provide a means of controlling blood levels of the active ingredient, and also provide greater efficacy, safety, patient convenience and patient compliance. Unfortunately, the instability of most proteins (e.g. denaturation and loss of bioactivity upon exposure to heat, organic solvents, etc.) has greatly limited the development and evaluation of sustained-release formulations.
Biodegradable polymer matrices have thus been evaluated as sustained-release delivery systems. Attempts to develop sustained-release formulations have included the use of a variety of biodegradable and non-biodegradable polymer (e.g. poly(lactide-co-glycolide)) microparticles containing the active ingredient (see e.g., Wise et al., Contraception, 8:227-234 (1973); and Hutchinson et al., Biochem. Soc. Trans., 13:520-523 (1985)), and a variety of techniques are known by which active agents, e.g. proteins, can be incorporated into polymeric microspheres (see e.g., U.S. Pat. No. 4,675,189 and references cited therein).
Utilization of the inherent biodegradability of these materials to control the release of the active agent and provide a more consistent sustained level of medication provides improvements in the sustained release of active agents. Unfortunately, some of the sustained release devices utilizing microparticles still suffer from such things as: active agent aggregation formation; high initial bursts of active agent with minimal release thereafter; and incomplete release of active agent.
Other drug-loaded polymeric devices have also been investigated for long term, therapeutic treatment of various diseases, again with much attention being directed to polymers derived from alpha hydroxycarboxylic acids, especially lactic acid in both its racemic and optically active form, and glycolic acid, and copolymers thereof. These polymers are commercially available and have been utilized in FDA-approved systems, e.g., the Lupron Depot(trademark), which consists of injectable microcapsules which release leuprolide acetate for about 30 days for the treatment of prostate cancer.
Various problems identified with the use of such polymers include: inability of certain macromolecules to diffuse out through the matrix; deterioration and decomposition of the drug (e.g., denaturation caused by the use of organic solvents); irritation to the organism (e.g. side effects due to use of organic solvents); low biodegradability (such as that which occurs with polycondensation of a polymer with a multifunctional alcohol or multifunctional carboxylic acid, i.e., ointments); and slow rates of degradation.
The use of polymers which exhibit reverse thermal gelation have also been reported. For example, Okada et al., Japanese Patent Application 2-78629 (1990) describe biodegradable block copolymers synthesized by transesterification of poly(lactic acid) (PLA) or poly(lactic acid)/glycolic acid (PLA/GA) and poly(ethylene glycol) (PEG). PEGs with molecular weights ranging from 200 to 2000, and PLA/GA with molecular weights ranging from 400 to 5000 were utilized. The resultant product was miscible with water and formed a hydrogel. The Okada et al. reference fails to provide any demonstration of sustained delivery of drugs using the hydrogels.
Cha et al., U.S. Pat. No. 5,702,717 (Dec. 30, 1997) describe systems for parenteral delivery of a drug comprising an injectable biodegradable block copolymeric drug delivery liquid having reverse thermal gelation properties, i.e., ability to form semi-solid gel, emulsions or suspension at certain temperatures. Specifically, these thermosensitive gels exist as a mobile viscous liquid at low temperatures, but form a rigid semisolid gel at higher temperatures. Thus, it is possible to use these polymers to design a formulation which is liquid at room temperature or at lower temperature and below, but gels once injected, thus producing a depot of drug at the injection site. The systems described by Cha et al. utilize a hydrophobic A polymer block comprising a member selected from the group consisting of poly(xcex1-hydroxy acids) and poly(ethylene carbonates) and a hydrophilic B polymer block comprising a PEG. The Cha et al. system requires that less than 50% by weight hydrophobic A polymer block be utilized and greater than 50% by weight hydrophilic B polymer block be utilized. Interestingly, however, it appears that several of the disclosed hydrogels might not be commercially useful in that the lower critical solution temperature (LCST) for many of the gels is greater than 37xc2x0 C. Although Cha et al. propose use of their hydrogels for controlled release of drugs, no such demonstration is provided.
Martini et al., J. Chem. Soc., 90(13): 1961-1966 (1994) describe low molecular weight ABA type triblock copolymers which utilize hydrophobic poly(xcex5-caprolactone)(PCL) and PEG. Unfortunately, in vitro degradation rates for these copolymers was very slow, thus calling into question their ability as sustained-release systems.
Stratton et al., PCT/US97/13479 (WO 98/02142) Jan. 22, 1998, describe pharmaceutical compositions comprising a polymeric matrix having thermal gelation properties, for the delivery of proteins. The class of block copolymers described are generically referred to as polyoxyethylene-polyoxypropylene condensates (also known as Pluronics). Unfortunately, systems utilizing Pluronics suffer from the fact that they are toxic to body organs and are nonbiodegradable. Moreover, only high molecular weight Pluronics at higher concentrations (25-40 wt. %) exhibit thermoreversible gelation.
It is thus the object of the present invention to provide thermosensitive, biodegradable hydrogels for the sustained delivery of drugs such as leptin. The hydrogels of the present invention utilize copolymer compositions which provide for instant gelation, and which possess the necessary rate of degradation to make use of the hydrogels commercially practical.
In one embodiment, the present invention provides pharmaceutical compositions comprising an effective amount of a biologically active agent incorporated into a polymeric matrix, said polymeric matrix comprising a block copolymer which is biodegradable, exhibits thermal gelation behavior, and is capable of providing for the sustained-release of the biologically active agent. Importantly, the leptin containing pharmaceutical compositions of the present invention result in no kidney anatomical abnormalities, improve the solubility properties of the leptin at physiological pH, increase the stability of the leptin protein, provide for improved efficacy, and result in no adverse injection site reactions associated with leptin precipitation at the injection site.
In another embodiment, the present invention provides a method for the parenteral administration of a biologically active agent in a biodegradable polymeric matrix to a warm blooded animal, wherein a gel depot is formed within the body of said animal and the biologically active agent is released from the depot at a controlled rate concomitant with biodegradation of the polymeric matrix.